PSI - Issue 64

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Abheetha Peiris et al. / Procedia Structural Integrity 64 (2024) 588–595 Peiris, Harik, et.al. / Evaluation of Historic Truss Bridges 00 (2019) 000–000

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3. Historical importance factor, HIF The Historical Importance Factor (HIF) identifies historic truss bridges requiring priority in rehabilitation and/or preservation. HIF is based on four factors, and for each factor, a bridge is assigned a weighted score based on pre specified criteria. The four factors are: • Unique Truss Factor ( X 1 ) • Age Factor ( X 2 ) • Unique Feature Factor ( X 3 ) • Historic Feature Factor ( X 4 ) The HIF is calculated by multiplying these four independent factors (Eq. 1) rather than summing them. It was decided that the product will better highlight/identify the historically important bridges. HIF = X 1 ꞏ X 2 ꞏ X 3 ꞏ X 4 (1) 3.1. Unique truss factor, X 1 A wide range of truss type bridges need to be preserved. Table 1 shows the number of trusses classified within each truss type among the bridges selected for prioritization. The total truss count of 105 is more than the 94 bridges under consideration since several bridges have multiple spans with different truss types. The last two remaining Bedpost trusses were among the bridges that were replaced during the study period. Accordingly, this truss type is not listed in Table 1.

Table 1. Truss types and number of trusses per type Truss Type

Number of Trusses

% of Total Trusses

Pratt Through Warren Deck

19 12 11 10

18.1 11.4 10.5 9.5 8.6 8.6 4.8 3.8 3.8 3.8 2.9 2.9 2.9 1.9 1.9 1.9 0.9 0.9 0.9 100

Continuous Warren Through

Pratt Pony

Parker Through

9 9 5 4 4 4 3 3 3 2 2 2 1 1 1

Polygonal Warren Through (with verticals)

Pratt Half-Hip Pony Camelback Through

Warren Pony (with verticals) Warren Through (with verticals)

Bailey

Pennsylvania (Petit) Through

Polygonal Warren Pony (with verticals)

Baltimore Through

Pratt Deck

Whipple

Baltimore Deck Bow String Arch

Parker Pony

Total

105

Table 2 summarizes the weighted values for the Unique Truss Factor ( X 1 ). The magnitude of the factor is based on the remaining number of trusses in a particular truss type. The smaller the number of bridges with a certain truss type, the larger the factor.